1. Field of the Invention
The invention relates generally to illuminated signs having multiple point light sources such as light emitting diode arrays as the illumination source for legend-bearing face panels and particularly to diffuser structure mountable in relation to such an array for facilitating an even distribution of light within such a sign to improve illumination of the typically translucent legend disposed on such a face panel.
2. Description of the Prior Art
Illuminated signs and particularly exit signs are commonly employed in commercial and industrial situations as well as in multi-unit residential buildings primarily for exit identification. Such signage takes many forms with interior illumination being provided through the use of a variety of illumination sources, an illumination source of particular utility in these energy conscious times being light emitting diodes which require greatly reduced power expenditures for operation. Although light emitting diodes have been used as the illumination source in exit signs and the like for well over twenty years, the use of light emitting diodes as the illumination source in an exit sign or the like continues to have negative aspects due primarily to the low level of illumination provided by a single diode. While developments in the production of light emitting diodes have continued over the years toward greater light-producing levels for these devices, it must still be recognized that LED technology has not improved to the present time to a point where only a few diodes could be employed with the lighting efficiency of, for example, only one or two incandescent or fluorescent lamps such as are also presently used in exit signage and the like. In order to overcome the low light generating capability of presently available light emitting diodes, various approaches have evolved including the use of a relatively large number of spaced apart light emitting diodes in various arrangements or arrays for providing the necessary candle power for satisfactory illumination of the interior of an exit sign such that the legends on face walls of such signs are evenly illuminated according to code requirements or any other reasonable standard of acceptability. In many such signs, light emitting diodes have been arranged in rows corresponding to the configuration of letters or numbers which comprise the legend of the sign. Such arrangements typically produce alternating bright spots and dark spots in the illuminated legend of the sign even when a diffuser material is placed between the light emitting diodes and the legend sheet or plate. The use of diffusing structure and of reflecting structure has also come into practice in efforts to more evenly distribute light within an exit enclosure so that a legend sheet or plate is more evenly illuminated and illuminated with sufficient candle power to provide an illuminated sign of satisfactory utility. As one example, Rycroft et al, in U.S. Pat. No. 5,365,411, provides diffusing structure in the form of coatings intended to diffuse light emanating from light emitting diodes prior to exit of the light from the sign enclosure through a translucent legend. In patents such as U.S. Pat. No. 5,276,591 to Hegarty, diffusing structure is provided to facilitate use of light emitting diodes and illumination sources in exit signs or the like wherein the diodes are placed to cause light from the diodes to take an indirect path through the translucent legend portion of a legend sheet or plate. In Hegarty, transparent or translucent plastic panels are employed which are edge-lit by linear arrays of light emitting diodes so that light injected into the edges of the plastic panels is reflected internally therewithin to diffuse the light and thereby to attempt the creation of an acceptable and even level of illumination within the sign enclosure.
The history of light emitting diode usage in exit signs has therefore been and continues to be an attempt to engineer the use of as few diodes as possible combined with diode mounting arrangements, reflector arrangements and diffuser arrangements inter alia which will provide an acceptable illumination level coupled with a desired even illumination within an acceptably compact sign enclosure structure. Recent trends toward placement of linear LED arrays along one or more interior perimetric walls of a sign enclosure has typically been accompanied by objectionable bands of differing brightness levels horizontally across the illuminated legend of such a sign, such signs so lit often failing to meet code requirements for visibility in addition to being aesthetically objectionable. Prior attempts to correct this particular problem have typically involved positioning of the LED array at greater distances outside of the extents of the translucent legend portions of the sign panel, thereby increasing size and cost of the sign enclosure.
The present invention intends improvement upon the prior art by provision of a volumetrically compact sign enclosure evenly illuminated throughout the interior of the enclosure by an array of light emitting diodes preferably disposed along one interior wall of the sign enclosure. Preferably, a linear array of a minimum number of light emitting diodes is disposed along the horizontal "floor" of the exit sign with the light emitting diodes being mounted to a substrate such as a printed circuit board and extending upwardly from the printed circuit board, which board is positioned immediately below the location of the translucent portions of the legend disposed in or on a sign panel or sheet of the exit sign. The invention particularly contemplates use of a diffuser element mounted above the LED array and being configured to scatter or diffuse light from the light emitting diodes near lower portions of the sign panel and to allow undiffused passage of light through at least portions of the diffuser and into portions of the sign enclosure located both medially of the enclosure and adjacent opposite wall portions of the enclosure. A desirable illumination level and evenness of illumination is therefore provided within the sign enclosure to evenly illuminate the sign legend at an acceptable level of brightness. The advances in the art afforded by the present invention are accompanied by a reduction in the number of light emitting diodes necessary to produce a given illumination level coupled with an ability to provide a compact sign enclosure, manufacturing costs of the exit enabled by the features of the invention thus being held to acceptable levels.